The microelectronics industry is continuously scaling down feature sizes and developing new material applications in the pursuit of smaller and faster devices. One focus towards this goal is the implementation of copper into multi-level interconnect schemes for microprocessor and memory devices as copper offers improved electromigration resistance and higher electrical conductivity versus aluminum-based interconnects. The semiconductor industry is introducing copper interconnects as a replacement for conventional aluminum and aluminum alloy interconnects for future generations of semiconductor devices. With its greater current carrying capacity, the introduction of copper interconnects should reduce device geometry, power consumption and heat generation. However, copper is a fast diffuser in silicon and diffuses in dielectrics, resulting in a deterioration of devices at low temperatures. To avoid unwanted migration of copper atoms, the copper wiring should be encapsulated with a barrier layer, e.g., barrier diffusion layer, to prevent diffusion of copper. The encapsulation of copper wiring is commonly done using a combination of an underlayer of a low-resisitivity transition metal-based material and an insulating layer comprised of a Si-based film. Each of these barriers may be comprised of more than one material to maximize properties and performance, i.e. a bilayer of Ta/TaN or bilayer of SiNx/SiCxNy. In order to minimize the capacitance contribution of the insulating diffusion barrier to the RC time delay, a desirable insulating barrier may have a low dielectric constant, k, to limit overall capacitance when integrated into the interconnect design.
One method of providing the insulating barrier layer is through plasma enhanced chemical vapor deposition (PECVD). Thermal chemical vapor deposition (TCVD) is a process in which a flow of gaseous reactants over a heated semiconductor substrate chemically react to deposit a solid layer on the heated substrate. PECVD is a process which introduces a plasma to activate the gaseous reactants. In each case, the flow of the reactants can be in parallel or in series, whereby a series flow of reactants is sometimes referred to as atomic layer deposition.
One current manufacturing technology for producing an insulating barrier layer generally is transitioning from plasma enhanced chemical vapor deposited (PECVD) SiNx to PECVD SiCxNy and SiCx because these materials generally have a lower dielectric constant. Recent studies have reported PECVD SiCxNy films with dielectric constants of approximately 5 and PECVD SiCx films with a dielectric constant less than 5, resulting in an approximately 25% lower a dielectric constant compared to PECVD SiNx. See, Martin et al., 2002 IEEE International Interconnect Technology Conference, Burlingame, Calif., Jun. 3–5, 2002, 42; and Fayolle et al., 2002 IEEE International Interconnect Technology Conference, Burlingame, Calif., Jun. 3–5, 2002, 39. However, PECVD film deposition can cause damage to the bulk insulating material, commonly referred to as the intermetal/intrametal dielectric. Also, current Si-based PECVD films may not meet future performance requirements, such as adhesion to other interconnect films, electromigration performance with copper, barrier properties, or low current leakage.
Additionally, boron has been utilized in high density plasma chemical vapor deposition. See, U.S. Pat. No. 6,500,771. U.S. Pat. No. 5,895,938 illustrates semiconductor devices using semiconductor boron carbo-nitride compounds such as a light-emitting device and a solar cell. The '938 patent illustrates a CVD process to form a boron carbo-nitride compound to grow into a crystalline structure wherein a substrate temperature at 850° C. or more was used in the step of forming the boron carbo-nitride compound. U.S. Pat. No. 6,424,044 shows a method of forming a boron carbide layer formed in a PECVD for use as a barrier and an etch-stop layer in a copper dual damascene structure. U.S. Pat. No. 6,352,921 illustrates amorphous boron carbide is formed in a PECVD for use as a barrier and an etch-stop layer in a copper dual damascene structure. U.S. Pat. No. 6,288,448 a process of combining silane and ammonia in a boron rich atmosphere for semiconductor interconnect barrier material for use with copper interconnects.
BCx and BCxNy films have been reported with a dielectric constant ranging from 3 to 7. See, Sugino et al., Applied Physics Letters, Vol. 80, No. 4, 649; Gelatos et al., MRS, Vol. 260, 1992, 347; Levy et al., MRS, vol. 427, 1996, 469; and Nguyen et al., J. Electrochem. Soc., Vol. 141, No. 6, 1994, 1633. For the deposition of boron carbo-nitride films using dimethylamine borane (DMAB), the increase in the dielectric constant with increasing temperature may be caused by a higher atomic density in the films that leads to a higher polarizability. Sugino, et al., observed an increase in the dielectric constant with temperature for films deposited by PECVD using BCl3/N2/CH4, while Gelatos, et al, observed a higher temperature with a decreasing dielectric constant for PECVD films using B2H6/NH3.